We have previously shown that a wide variety of virally and spontaneously transformed mammalian fibroblasts secrete a major transformation-dependent phosphoprotein with a molecular weight of about 62,000. Elevated secretion of the phosphoprotein occurs regardless of the transforming agent and secretion is temperature sensitive in a cell line that is temperature sensitive for the transformed phenotype. Elevated secretion of this major phosphoprotein also correlates with tumorigenicity of cells of epithelial origin and distinguishes neoplastic from hyperplastic epithelium. The 62K phosphoprotein is apparently not related to viral or tumor-specific phosphoproteins which have been described by others. Recently, I have determined that the 62K secreted phosphoprotein binds avidly to fibrin clots, binds selectively to lysine and benzamidine-Sepharose, and shares antigenic determinants with a component of normal plasma and serum. Because fibrin deposition commonly accompanies tumor growth in vivo, it may be that the 62K phosphoprotein associates with tumor-fibrin in vivo. The goals of this proposal are to purify the 62K phosphoprotein extensively, to characterize it biochemically, to determine its biological functions, and to relate these properties to the biology of tumor growth. The affinity of the phosphoprotein for fibrin clots will be analyzed further, and it will be determined if the phosphoprotein is related to any of the proteins with known affinities for fibrin. Purified preparations of the phosphoprotein will be analyzed for proteolytic activity, and the effect of dephosphorylation on this activity (if found) as well as the phosphoprotein's affinity for fibrin will be examined. Antibody to the 62K phosphoprotein will be used to purify the antigenically related component(s) of plasma and serum and they subsequently will be characterized. Metabolic labeling of tumor-bearing animals and immunofluorescent staining of tumor sections will be employed to study the expression and localization of the phosphoprotein in vivo. Finally, additional tumorigenic and nontumorigenic cells (including human) will be compared for secretion of the phosphoprotein to further test its apparent correlation with tumorigenicity.